The answer:
Then rushing sudden on his prostrate prize,
To spoil the carcase fierce Patroclus flies:
Swift as a lion, terrible and bold,
That sweeps the field, depopulates the fold;
An epic simile is a figurative language or a metaphor that uses comparisons to describe an event, someone, a place, etc. by using the words "like", "as" or "as in" and that is developed over several lines of verse, and which it's more commonly found in epic poems (The Illiad is a good example of it). Its aim is to make the writing more colorful and interesting and serve as decoration.
The excerpt uses simile to describe the character as bold and terrible, the word "as" is key to identify it as a simile and not other literary devices. Here are the lines that best illustrate the use of the epic simile:
"Swift as a lion, terrible and bold,
That sweeps the field, depopulates the fold"